Modern vehicle engines may use a heat transfer fluid (e.g., liquid coolant) to provide long-lasting, year-round protection of their cooling systems. A key function of heat transfer fluids is to transfer excess heat from an engine to a radiator for dissipation. Efficient heat transfer and control of engine temperature leads to efficient fuel economy and lubrication, and may prevent engine failures due to freeze-up, boiling-over, or over-heating. Ideally, engine coolant may also serve to provide corrosion protection of cooling system metals (e.g., over a range of different temperature and operating conditions).
Common corrosion-related problems that may arise in automotive cooling systems include: (1) cavitation corrosion and rusting of cylinder heads and cylinder blocks; (2) seal leakage, bellows seal failure, and cavitation corrosion in water pumps; (3) solder bloom, scale and deposit formation, and pitting in radiators and heater cores; (4) thermostat sticking; and/or (5) crevice corrosion at hose necks. In addition, erosion-corrosion, galvanic corrosion, under-deposit corrosion, and/or stray-current corrosion may occur at susceptible locations in a cooling system depending on conditions.
Different kinds of metals may be used to fabricate the various parts of a cooling system. By way of example, cast iron and cast aluminum alloys may be used for cylinder blocks, cylinder heads, intake manifolds, coolant pumps, and power electronic device enclosures; wrought aluminum and copper alloys may be used for radiators and heater cores; solders may be used to join the components of brass or copper radiators or heater cores; steel may be used for cylinder head gaskets and for small components such as freeze plugs, coolant pump housing enclosures, and coolant pump impellers; and copper alloys may be used in thermostats.
Corrosion protection of components manufactured from aluminum or aluminum alloys (e.g., engine block, cylinder head, water pump, heat exchangers, and the like), corrosion protection of heat transfer system components produced by a controlled atmosphere brazing (CAB) process (e.g., heat exchangers), and corrosion protection at high temperature (e.g., in cooling systems for vehicles equipped with exhaust gas recirculation or EGR) are of particular interest.